Feature suggestion: command to generate default configuration

[confluence]

It would be useful for the controller to generate default controller and optionally global backend configuration, and possibly do this during installation.

It's unfortunate that the JSON format doesn't support comments; best practice would be to comment out all the defaults and allow the user to uncomment fields to change. Inline comments would also make the file self-documenting. But a generated file would still be an improvement over copying and pasting from the docs or hand-coding JSON from scratch.

Could we add some magic to detect the locations of the executables and frontend, so that these fields default to the correct values? If multiple options are found, the user could be prompted to select one (a flag should be available to accept the first one automatically).

Followup: it would be nice if we could also generate individual default config files for authentication providers.

[confluence]

I see that we're already parsing the config file as JSONC. That means that we could in fact generate a full self-documenting configuration file with most properties commented out. I will see if I can create a suitable default for the docs.

[confluence]

Trailing commas are not standard JSONC (there is no standard JSONC), but the library we use allows them, so we should be good to go.

[confluence]

Possible issue: the backend uses standard JSON parsing, so we can't use comments / trailing commas in the backend config unless we change that.

Here's a JSONC library for C++.

Alternatively, we could pre-parse the file to remove comments (easy) and trailing commas (less easy?).

nlohmann/json supports ignoring comments and will also support trailing commas when this PR is merged. So if we wait, this should be a simple change. We should probably target the stable release with this.